Prevent dupicate keys in dictionaries

yaml_load_and_assert_uniqueness.py

"""
Copyright 2024 Dustin Oprea

MIT LICENSE

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in the Software without restriction, including without limitation the rights
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SOFTWARE.
"""

import yaml


class _UniqueCheckedLoader(yaml.SafeLoader):

    def construct_yaml_map(self, node):

        # If we're here, we're definitely constructing a map and have a list
        # of child nodes

        keys_s = set()
        duplicated_keys_s = set()
        for child in node.value:
            child_key, child_value = child

            before_count = len(keys_s)
            keys_s.add(child_key.value)
            after_count = len(keys_s)

            if after_count == before_count:
                duplicated_keys_s.add(child_key.value)

        if duplicated_keys_s:
            raise \
                Exception(
                    "One or more map keys are duplicated: {}".format(
                    sorted(duplicated_keys_s)))


        data = {}
        value = self.construct_mapping(node)
        data.update(value)

        yield data


def load_and_assert_uniqueness(x):

    # We'd like to detect duplicates. Since PyYAML both loads things depth-first
    # *and* doesn't give us the parent when processing a child node, we'll index
    # of all of the object IDs as we're constructing them, and then see which
    # are disappeared from the final hierarchy. Since all we can do is pass a
    # class, we need to inline the class in order to load into an index within
    # our scope.
    #
    # We're only concerned about dictionary keys with dictionary values because
    # a) this is our use-case, and b) we can stash additional information as
    # dictionary keys without having to override any types.

    _UniqueCheckedLoader.add_constructor(
        'tag:yaml.org,2002:map',
        _UniqueCheckedLoader.construct_yaml_map
    )


    # Load

    blob = yaml.load(x, Loader=_UniqueCheckedLoader)
    return blob